An MRI apparatus is an apparatus for observing the inside of a patient by acquiring a tomogram and a frequency spectrum of a patient making use of a nuclear magnetic resonance phenomenon and includes a static magnetic field generator, a gradient magnetic field coil, a transmitting coil, and a receiving coil. The static magnetic field generator aligns the directions of the spins of nuclei (ordinarily, protons) that constitute the patient, the gradient magnetic field coil identifies the imaging slice of the patient as well as encodes position information to the nuclear magnetic resonance signals acquired from the patient, the transmitting coil generates a high frequency magnetic field having the same frequency as the resonance frequency of the protons, and the receiving coil receives the signals from the protons.
The MRI apparatus arranged as described above can selectively image any of arbitrary regions and tissues, and various imaging methods have been proposed according to patients to be imaged. For example, imaging can be executed using a two- or three-dimensional measurement. Further, in recent years, as an important field to which the MRI apparatus is applied, there has been developed a method (IV-MRI) of utilizing the MRI apparatus as the monitor of a catheter while needling or introducing the catheter into a blood vessel. In this IV-MRI, it is required to execute imaging and to display images in real time so that, for example, the catheter can be inserted to a target position without fail, and various types of a high speed imaging method such as EPI and the like have been in practical use.
In contrast, various shapes of the receiving coil have been developed and practically used according to portions to be imaged, and an RF receiving antenna, which also acts as a guide wire of the catheter, has been proposed as a receiving coil preferably used when the catheter is inserted as described above (for example, Japanese Unexamined Patent Publication No. 10-179550, PCT Japanese Translation Patent Publication No. 2000-509276, a document “Intravascular Magnetic Resonance Imaging Using a Loopless Catheter Antenna”, MRM 37: 112-118 (1997), and the like). Note that since the measurable sensitivity range of the guide-wire-shaped RF receiving antenna is limited to the vicinity of the guide wire, a tomogram that can be imaged is limited to a small region (for example, several millimeters).
However, an image obtained by conventional MRI apparatuses is mainly a tomogram. Accordingly, the conventional MRI apparatuses are disadvantageous in an application for confirming the position of a catheter inserted into a body cavity such as a blood vessel having a curving portion because they cannot uniquely determine a sliced plane including the catheter. In contrast, as to a straight needle, the conventional MRI apparatuses can automatically take a tomogram on a plane including the needle or on a plane orthogonal to the needle by attaching an active or passive marker to the needle, and many conventional technologies exist. Further, as to the catheter, there is known a method of executing imaging by providing a marker, which can be identified by the MRI apparatuses, in the catheter. Since, however, a sliced plane including the catheter having a curved portion cannot be uniquely determined, it is not always easy to confirm the inserted position of the catheter.
Incidentally, the applicant has proposed a method of creating an endoscope-like image making use of three-dimensional image data acquired by an X-ray CT apparatus and an MRI apparatus as a method of displaying an image of the inside wall of a blood vessel, and the like in place of a conventional tomogram (Japanese Unexamined Patent Publications Nos. 7-210704 and 8-16813). According to the method, it is possible to convert three-dimensional tomogram data of a region including a blood vessel and the like into an image (endoscope-like image) of the inside wall of a body cavity, and the like observed from the inside by a center projecting method and to display the image, and this image is effective to diagnosis. In this case, the image may be processed according to particular shading algorithm.
However, the conventional endoscope-like image is created by a method of creating it based on three-dimensional image data that has been acquired, and further a view point and a line-of-sight direction must be input by a mouse or a track ball. Accordingly, the method cannot be applied to the IV-MRI which executes imaging and display of an image in real time.